Electron tube circuits



March 28, 1939. K, W, ARWS ET AL 2,151,771

ELECTRON TUBE CIRCUITS ,Filed April 10, 1935 2 Sheets-Sheet l AHEIIIFHELLII March 28, 19 9. K. w. JARVIS ET AL 2,151 771 I ELECTRON TUBE CIRCUITS Filed April 10, 1935 2 Sheets-Sheet 2 Patented Mar. 28, 1939 Z,l5l,77l

ELECTRON TUBE cmcnrrs Kenneth W. Jarvis, New Rochelle, N. Y., and Russell M. Blair, Teaneck, N. J., assignors to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application April 10, 1935, Serial No. 15,712

13 Claims. 179-171) The present invention relates to circuit arsources and methods of obtaining emission may rangements particularly adapted for use in consuitably be used. In such a case, control elenection with the operation of electron and vacments other than the grid structure shown at 3 uum tubes of the general types described and might be used, such as light intensity in case of 5 claimed in our issued U. .8. Patent No. 1,903,569. photoelectric emission, etc. The emission from Still further and more particularly this inventhe cathode 5 is indicated by the arrows 6 and is tion relates to the use of primary and secondary directed toward a collector plate I, which in turn emission electron streams and associated .tube is connected back through the potential source 8 and circuit elements and operating potentials, for to the cathode 5. Under proper conditions, to be can" '10 producing systems having a high degree of operhereinafter described, secondary charges are 1'0" ating efficiency and stability. A further object emitted from the collector plate I and directed as of our invention is to provide an electronic amindicated by the arrows 9 toward the output plate plifier device capable of producing high gains over l0. It should be understood at this point that frequency ranges varying to all practical intents the term charges herein used is to be regarded and purposes from zero to infinite frequency and as generic and includes electronic emission, pro- 15 especially suitable where extremely high fretonic emission and/or any charged body. The quencies are involved. Still further objects are charges gathered by the output plate I 0 are to provide an amplifying system whereby the acpassed through the load network, which in this tion of the tube and the associated circuits may case consists of an inductance II and a con- 7 be made substantially independent each from denser l2, and then through the source of poten- 20 the other. Other and further objects may be tial l3 back to the cathde 5. The shield I4 is observed in the following description. interposed to prevent the flow of the cathode The general relationship of the electrode strucemission 6 directly to the output plate In without ture in such types of electron tubes as will be having the relay action taking place at the colnr' utilized to describe the essentials of this invenlector plate 1. The shield may be connected to tion as applied to various circuit arrangements the cathode 5 by the source of potential I5.

are set forth in our U. S. Patent No. 1,903,569, and Fig. 2 shows the current flowing in the cathode various forms of the circuits suitable for operatat the point It with respect to the potential aping such a tube are shown by the drawings, plied to the collector plate I by means of the wherein, source of potential 8, the potentials on other elec- 3'0 1 '0 Fig. 1 is a circuit diagram, including an electrodes being maintained constant. Asthe potentron tube toserve as a portion of our amplifying tial E8 is raised, the current I16 increases, possisystem; bly following reasonably near the well known Figs. 2, 3, 4 and 5 are curves showing the relathree halves power law, between the points I! tion of certain potentials and currents; and "5. Above !8, however, the current flattens 5 Fig. 6 portrays another operative combination out as shown from l8 to l9, instead of continuof tube and circuit elements; ing on its original trend of H to l8 to 20. This Fig. '7 shows a control element acting to influflattening is well known in the case of thermal ence a secondary emission current stream, and emissive bodies, and is due to the fact that the Fig. 8 shows both the control elements of Figs. voltage E8 s sllfllc e y high t the Point 58 to 4.0 1 and 7 combined in a single operative structure draw over all the charges e at from th and system for simultaneous amplification of sevcathode (at this temperature of operation). eral frequencies. Further increase in voltage therefore cannot in A better understanding of the invention may crease I16 and we have a result called saturation. be had by making reference to the various figures (Temperature saturation, as a further increase of the drawings. Referring first to Fig. 1 thereof cathode temperature would increase the curof, the reference character l indicates the comrent I16.) plete tube structure, here shown in a simple dia- Considering the collector plate 1 as an emitting grammatic form. An input circuit indicated at body, a curve somewhat similar to that of Fig. 2 2, connects with a control element 3, and includes y be drawn. This curve, show i g. 3, is a polarizing battery 4, which is connected to the p t d be difiel'ent Steady potentials E13 cathode 5. While, as shown, the cathode is made applied to the output plate Ill and I21, the current, emissive by thermal means, no restriction is to through the point 2! in Fig. 1. In Fig. 3, the voltbe placed on the source of emission, and photo ages on other tube elements were held constant. electric, radio active, gas ionization or other The charges emitted from the cathode 5, acceler- 55 ated by the potential Es maintained on collector plate 1, strike the collector plate I at high velocity and drive off secondary charges. These secondary charges are emitted at low velocity and build up a space charge around the collector plate 7. When the potential of the output plate Ii! is zero or at a lower value than Es, these secondary charges fall back into the collector plate 1. Hence, in Fig. 3, the current I21 is substantially zero whenever E13 is less than Ea, as shown between the points 22 and 23. After the point 23, however, the current I21 rises to the point 24. Up to this point the increasing voltage on the output plate [0 draws over more and more of the low velocity secondary emission from the collector plate 7. At the point 24 substantially all of the secondary emission is taken over to the output plate It! and from the point 24 to point 25 in Fig. 3, saturation somewhat similar to that shown in Fig. 2 takes place. Inasmuch as a large number of secondary charges may be driven ofi for each primary charge, the maximum current I21 may be many times the cathode emis-,

sion I16. Beyond the point 25 a new effect comes into play. In increasing the potential E13 a gradually changing field pattern of the electrostatic lines of force takes place and the charges transversing the space between the cathode 5 and collector plate I are subjected to a strong diverting force as soon as they reach the region beyond the screening action of the shield I 4. The momentum acquired by the charges moving from the cathode 5 toward the collector plate "I is sufiicient, with E13 at a reasonably low value, to carry them on to the collector plate I and so give rise to the gain due to the secondary to primary emission ratio. There comes a value of E13, however, when these charges are diverted around the corner in spite of the protective action of the shield electrode I4, passing directly to the output plate iii. In this case, the secondary emission ratio gain of these particular charges is lost and I21 decreases, the limit being the point at which all the primary emission 6 would be pulled around the corner and 121 would drop to the value I16. It is obvious therefore that for maximum amplification it is desirable to work between the points 24 and 25. This will be referred to again.

Fig. 4 shows the secondary emission current 121 as a function of E8, when the potential E13 is always maintained within the range corresponding to the maximum value section 24--25 of the I21 curve shown in Fig. 3. The current I21 starts at the point 28 in Fig. 4 and increases rapidly towards the point 29. An initial value of E8 is required to produce secondary emission, it being seemingly necessary to impart more than a critical energy state to the particles in the primary emission stream to bring about the ejection of charges from the collector plate 1. Although the primary emission current no longer greatly increases after the point la in Fig. 2, the secondary emission ratio continues to go up with increase of potential E3. This increase does not appear to be indefinite and tests of numerous materials indicated that points can be reached where increasing the potential Es does not produce corresponding increases in secondary to primary emission ratio. The reason for this is somewhat obscure but the action is as though the emission of secondary charges was purely a surface phenomena, and after driving a primary charge against the collector plate 1 hard enough to make a (relatively) large surface splash, further force which might drive the incoming charge deeper,

would dislodge no more surface charges. The efiect is not likely one of saturation as an increase in number of primary charges (i. e. value of current) gives a corresponding increase in secondary emission.

Fig. 5 shows a customary curve of output current against reference volts Eg on the grid control element of Fig. 1. In all respects this is quite similar in appearance to the normal triode type of amplifier tube, except that the slope (mutual conductance) is multiplied by the secondary emission ratio. The saturation point 32 on this curve may be due to (temperature) saturation of the primary emission 6, or may be due to the limit of secondary emission l which will be drawn over to the output plate by reason of a too low voltage E13 on the output plate. (Similar to voltage saturation.) If the potentials are so chosen as to make these various limiting conditions outside the range of normal operation, an extremely satisfactory amplifier will result.

It will be noticed that the curve resulting from the saturation of the secondary emission from the collector plate I as shown by the curve between 24 and 25 of Fig. 3, is extremely fiat. This means no change of current I11 with output plate voltage E13 over this range, and consequently, infinite plate impedance. As this is a desirable condition of operation, a further precaution should be noted. Potentials existing across the output load or network, as here shown as inductance H and capacity l2, will add to and subtract from the potential E13. To operate between the points 24 and 25 of Fig. 3, it is therefore desirable to choose E13 sufii'ciently above the point 24 and sufii'ciently below the point 25, so that the variations in potential across the load in the output circuit cannot swing the actual potential on the output plate either below the point 24 or above the point 25.

Fig. 6 shows a multi element tube functioning in the same manner except that a plurality of opposed collector or electron-emitting plates are used to provide more than one step of secondary emission, thereby to still further increase the gain. In Fig. 6, the reference character 33 is used to designate the tube structure containing a cathode 34, a control element 35, a first collector plate 36, a second collector plate 31 and an output plate 38. Shields 39 and 40 are interposed to assist in providing desired potential gradients and to con- 1 trol the flow charges to the desired plates. Sources of potential 35, 39', 4!, 42, 43 and 44 are provided, which may largely be common if so desired, in order to obtain between the various elements the desired potentials. The inductance 45 and condenser 45 here form an output system, while the input system is indicated at 41. To obtain a desirable condition of amplification, we have found that the collector plate 3'! should be maintained at the saturation potential with reference to the collector plate 36, as shown between the points 24 and 25 of Fig. 3. The output plate 38 should also be so maintained with respect to the collector plate 31. The primary emission stream is indicated by the reference character 48, and the resulting secondary emission by the arrows 49. A second step of secondary emission results in the charge stream indicated at 50.

A number of important advantages result from the cooperating elements indicated in Fig. 6. It has been shown by others in the art, that capacity existing between the input and output elements of an amplifier is generally undesired as it may lead to oscillation or degenerative action. The greater the gain in an amplifier, the less such existing capacity must be'in order to avoid.

undesired effects. In the construction of Fig, 1,

practically all capacity coupling between the in put element 3 and the output. element Ill-is elim-.

inated by the action of the shield. 14. It is possible'to conceive, however, that if the gain of such an amplifier be increased enormously, the remaining capacity coupling .might reach an undesired 'point. The? construction and. associated circuits. andpotentials indicated in Fig.' 6 permitsuch an enormous gain, as, above-conceived, to .be obtained. In Fig. I, two elements, the collector plate 7 and the shield, fserve'to reduce the capacityjcouplinglbetween input and. output elements. In Fig. 6, four elements, collector plate'stfi and 31, and shields 39 and .40, serve to reduce any p'ossibleundesired efiects. Thus the same elements which, added to Fig, 1, serve to increase the gain, also reduce the-capacity coupling, and theinc'r'ease in gain is therefore. en-

tirely useful andwithout other deleterious effects. Another important advantage 'over present existing amplifiersis apparentin considering the cooperating elements'of Fig. ,6. In present known methods, an amplifyingtube'is controlled in some desired manner, the outputof thistube is transferred' to the control point of a succeeding. amplifier tube by means of an electrical network. This network occasionally has the advantage of adding frequency 'selectionto .thev amplifier (if desired) but may havecertain disadvantages among which may be power loss and reduction in eificiency of transmitted signal. Further, if a broadband. of frequencies is to be transmitted, it becomes exceedingly difiicultto design a translating networkto act between amplifying tubes so that the loss in such anetwork isnot'more.

than the gain in the amplifying tubes. Still'further, such. networks are, in general, of greater inefiiciencyatvery high frequencies and the probamplified. This. is especially useful for carrier current telephony, television, etc. where itmay be desirable to amplify several octaves innfrequency simultaneously.

A still further advantage is obtained in the cooperating system shown inFig. 6. It isnecessary in present types of amplifying. tubes tozhave rather large currents flow in the tube in order to make them good amplifiers. This is true even though the alternating. current components in such a tube used as the firstamplifier. are ex-. tremely small. The direct current component in that and subsequent amplifier tubes. should be equal to or greater than the peak alternating current value-to avoid cutofiwith sinusoidal currents. In the primary emission stream indicated as 48 in Fig. 6, only a small constant current need be provided; This is because the input signals, and the resulting alternating current component of the primary emission stream, is small. After being amplified by the secondary emission actionv at the collector plate 36.0f Fig. 6, the alternating currentcomponent is increased and for correct action, the direct current component must be increased also. However, the collector plate 36 amplifies alternating and direct current alike, and

hence, if a proper'ratio is obtained in the primary stream, no subsequent overloading can occur andnodistortion can result. As noted above, each branch. of the electron stream functions as a stage i of amplificationand the design of a multistage amplifier of the secondary emission type is thus materially simplified sinceprovision against overloading in the firststream branch or stage in sures against an overloading in any subsequent stream branch. This is particularly importantin the. case of a photoelectric source of primary emission, where the intensity and resultant pri-- mary emission stream may vary over wide extremes of value. i

A still further advantage is present in the sys-- tern of Fig. 6 as compared with the normal arm plifying system wherein successive amplifier tubes are coupled withelectrical networks. As is well known in the art, if a condenser is charged and then discharged into an electrical network'having 1.

less than a certain critical damping resistance, an oscillatory current results. In general, those networks used for coupling normal amplifier tubes have losses well below the critical damping point,

and so produce oscillatory currents whenever a condenser so discharges. As the condensers in suchnetworks are often charged due to transient electrical eiiects, they. equally often contribute undesired oscillatory discharges, causing such,

transients to hang over and producing more obviously disturbing results. Our method of am-.

plification, in eliminating such coupling networks between amplifying stages, eliminates such undesirable efiects asabove described.

Still other modifications of our amplifying device and system may be utilized as shown in Fig. I

'7. Here the-reference character 5i represents a tube structure, 52 a cathode or charge emitter, 53 is thecharge stream so emitted directed toward the collector plate 54 where a secondary charge stream 55 is developed by secondary emission action. This charge stream 55 flows towards the collector plate 56, where a new secondary emission charge stream 51 is produced, which in turn flows to the output plate 58. For the purpose of controlling the resulting charge streams at some point between the first point of origin and the last point of absorption, a control element 59' may be introduced at some point after the source of the first secondary emission stream, and is here shown interposed between the plates 54 and 56. This is a particular advantage when the initial source of primary emission as here represented by the cathode 52 is not a small localized sourcejbut is of such a nature as would be diificult to control bythe normal controlelement such as the grid structure shown. This arrangement is also advantageous whenever a changing field potential surrounding the emitter represented here as the cathode 52 will change the fundamentalnature, quantity, velocity, continuities of emission, etc. Such effects may be undesired, and as possibly caused by changes in potential of a con trol element, such a causation is eliminated by the interposition of the secondary emission relay action of the collector plate 5 and electrostatic shielding action of the shield 53. The secondary emission relay action on the collector plate 55,

and the electrostatic shielding of the interposed shield it, serve to completely separate the input grid control element and the output plate, thereby obtaining advantages previously described. Connected to the output plate is a load impedance network, here for example shown as inductance and condenser 6|. The input network is represented as the inductance 62. Sources of potential 63, B4, 65, 66, 61 and 68 serve to maintain any desired potential on the tube elements. The relative values of such potentials have been to some extent shown, but no limitation on the potentials desired is intended.

It is only a step from Fig. '7 to Fig. 8, where the noted tube structure, operating potentials and associated circuits permit simultaneous amplification of those frequencies associated with more than one source, for example, frequencies F1 and F2. In Fig. 8, the reference character ll por trays a substantially complete tube structure. The charge emitter, here shown as the cathode I2, produces the charge stream 13 directed toward the collector plate 14. This primary charge stream is subject to control, the means here shown as the grid structure 15. Secondary emission from the collector plate 74 is directed toward another collector plate T! as shown by the indicating arrows 76. Interposed between the collector plates is another control element, again a grid structure for modifying the secondary emission stream 16. Another stream of new secondary emitted charges comes from the collector plate H as indicated by the arrows 19. The output plate 80 absorbs and passes on this charge stream into the output network. As two separate controls are exercised on the charge streams within the structure, separate effects are produced. These may be separated (if desired) by a plurality of networks, each responsive to the initial frequency of control, such as frequencies F1 and F2. Such networks are as shown in the inductance 8! shunted by the condenser 82, and in the inductance 83 shunted by the condenser 34. One input circuit which actuates one control element is shown by the inductance 85, while a second input circuit which actuates a second control element is shown by the inductance 86. Sources of potential 81, 88 and 89 serve to maintain desired potential on the various tube elements. Electrostatic coupling between input control elements 15 'and 18 is prevented by the secondary emission relay action of the collector plate 74 and the electrostatic shielding action of the interposed shield 9!). Similarly, electrostatic coupling between either of these elements and the plate 80 is prevented by the secondary emission relay action of the collector plate 11 and the electrostatic shielding action of the interposed shield 9| In Fig. 8, when the various potentials are properly chosen, linear control eifects will result and substantial independence of amplification action of the two control elements will be obtained.

The methods of operation contemplated by our invention have been described with reference to certain specific circuits and applications. modifications and uses of the invention other than those herein described fall within the spirit of our invention as set forth in the following claims.

We claim:

1. An electron tube amplifying system comprising an input circuit, an output circuit, an electron tube relay device having a primary electron emitting electrode, an output electrode, and a plurality of electrodes intermediate the primary electron emitting electrode and the output electrode, said intermediate electrodes being adapted when sub- J'ected to the action of an impinging electron stream to emit secondary electrons, polarizing means including a voltage source having the positive terminal thereof connected to the output electrode and the negative terminal thereof connected with the primary electron emitting electrode, a plurality of independent connections between each of said intermediate electrodes and said voltage source whereby progressively increasing positive voltages relative to the primary electron emitting electrode may be applied to said intermediate electrodes to cause the development of an electrostatic field within the tube causing the electrons to move progressively from the source to the output electrode and to vary in number in accordance with the number of intermediate electrodes and the secondary emission factor of each, a shield electrode adjacent each intermediate electrode, and connections between the respective shield electrodes and the said polarizing means to apply a positive voltage upon each shield electrode of predetermined value rela tive to each adjacent intermediate electrode.

2. The system claimed in claim 1 comprising in addition a control electrode and a connection between said control electrode and one of said circuits to control the output from the system.

3. The system claimed in claim 1 comprising in addition a control electrode connected with the input circuit to control the output from the system in accordance with signalling impulses applied to the input circuit.

4. In an amplifier system, the combination with a tube including means for establishing a stream of electrons, a plurality of spaced electrodes adapted to release secondary electrons, a collecting electrode, control grids in the path of the electron stream to said collecting electrode and separated from each other by at least one of said spaced electrodes, a source of polarizing potential and connections from said potential source to the several spaced electrodes and said collecting electrode to establish a potential gradient from one to another of said spaced electrodes with a maximum potential at the collecting electrode, of a plurality of input circuits, an output circuit connected between said collecting electrode and said stream-establishing means, and means connecting each of said input circuits to an individual control grid.

5. In the operation of an amplifying system including a tube having a plurality of electrodes adapted to emit secondary electrons to form a series of successive streams of secondary electrons between a source of primary electrons and a collecting electrode, and a plurality of input circuits having different frequency characteristics, the method of controlling the output at the collecting electrode by the several input circuits which comprises modulating different streams of secondary electrons by the fluctuating voltages developed in the several input circuits.

6. In combination, means for producing a primary electron stream, means including opposed electrodesurfacesforproducingsuccessivestreams of secondary electrons of progressively increasing amplitude from said primary electron stream, a circuit for imparting to one of said electron streams an alternating current frequency characteristic, and an output circuit in which said electron streams develop an alternating current of a frequency controlled by said first circuit.

7. In the process of multiple amplification by the repeated development of streams of secondary electrons from electrode surfaces located between a source of electrons and an output electrode, the method of controlling the magnitude of the electron stream reaching said output electrode which comprises individually controlling the magnitude of the streams of electrons approaching different electron surfaces.

8. In an electron tube circuit, the combination with a tube including a pair of opposed electrodes each adapted to liberate electrons by secondary emission, means for establishing between said opposed electrodes an electrostatic field for attracting electrons from one electrode to the other, and means including a load circuit external to said tube for utilizing the current resulting from said electron movement, of means including a circuit element external to said tube for determining the frequency of the alternating voltage established by the movement of electrons from one electrode to the other.

9. The combination with an electronic tube, means within the tube for establishing a stream of primary electrons, and a plurality of opposed electrode means for receiving said electron stream and amplifying the same in the form of emitted secondary electrons, of an output circuit connected to at least one of said opposed electrode means, a circuit external to said tube in which an alternating voltage may exist, and means including said second circuit for controlling the magnitude of the electron stream.

10. An electron tube amplifying system ,comprising the combination with an electron tube device having a primary electron emitting electrode, an output electrode, and a plurality of electrodes intermediate said emitting and output electrode, said intermediate electrodes being opposed to and longitudinally spaced from each other and each having the property whenv subjected to an impinging electron stream of emitting secondary electrons, means including a source of polarizing potential external to said tube device and connections therefrom to said electrodes to establish an electrostatic field for moving a stream of electrons from said primary electron emitting electrode progressively to said intermediate electrodes and to said output electrode, whereby the number of secondary electrons arriving at said output electrode is dependent upon the number of intermediate electrodes and the secondary emission factor of each, an output circuit connected to said output electrode, and means including an input element external to said tube device for controlling the magnitude of the stream of electrons.

11. An electron tube amplifying system as claimed in claim 10, wherein said tube device includes a shield electrode adjacent certain of said intermediate electrodes, and circuit connections from said shield electrodes to said polarizing potential source for maintaining each shield electrode at a predetermined positive potential with respect to the adjacent intermediate electrode.

12. An electron tube amplifying system, as claimed in claim 10, wherein said magnitude controlling means comprises a control grid within said tube device and said input element is connected between said control grid and a tube electrode.

13. An electron tube amplifying system as claimed in claim 10, wherein said magnitude controlling means includes a plurality of input elements, and said tube device includes a plurality of control grids, each input element being connected to an individual control grid and said control grids being spaced apart along the electron stream by at least one intermediate electrode.

KENNETH W. JARVIS. RUSSELL M. BLAIR. 

